SA police say the exact location of a burnt out car in the circled area could provide the key to finding Karen Williams' remains.

Identifying the former location of a burnt-out car on the edge of Coober Pedy in South Australia's outback could be the key to finding the body of missing teenager Karen Williams.

Police say the body of the 16-year-old was hidden in the boot of the vehicle on the outskirts of the town for several days after she was murdered in 1990.

It is believed her body was removed a few days later and buried in a mineshaft within 20 metres of the car - possibly a white Ford sedan.

Several shafts were excavated in July near the intersection of Flathill Road and Malliotis Boulevard but there was no sign of Ms Williams' remains.

Superintendent Des Bray says the area has since been levelled and built on and the exact spot where the car once sat is unknown.

"It's critical to the success of this investigation to identify the exact location that vehicle was parked or abandoned. Clearly there would be somebody who owned that vehicle. There would be somebody who recovered the vehicle at a subsequent time from that site and would be able to tell us exactly where the vehicle was," he said.

"The vehicle would have been about five metres or less from the edge of the bitumen, so everybody driving past in Coober Pedy would have seen that vehicle. We're not looking for somewhere right out in the fields. We're looking at the edge of town at a T-junction, with a bitumen road.

"If we identify the owner of that vehicle and where that vehicle is, even though it's 23 years... the contents of the burnt out vehicle and the boot would probably be the same today from a forensic perspective and so there would be a very good chance of recovering forensic material."

Police have previously said the teenager was last seen in a Datsun 180B between 5:00am and 6:00am on August 4, 1990 and repeated a request for information about that vehicle.

The car is believed to have been sold or disposed of in the town or at Glendambo since Ms Williams' disappearance.

Police say the vehicle could still be in use and had the registration number SLG 539, but that could have changed.

Superintendent Bray says police have interviewed people from Sydney, Adelaide, Mount Gambier and Coober Pedy itself as part of the investigation, but says not all of those approached have been co-operative.

"There are some people seriously at risk of prosecution for impeding the investigation," he said.

Superintendent Bray remains says other mine shafts in the search area remain unexplored by police.

"Obviously no-one can go back and excavate those sites and steal any evidence because they're sixty feet deep," he said.

"I think we're in the best position to find her that we've ever been in.